The vascular events of penile erection involve the coordinated integration of the central and peripheral nervous systems. Penile erection is jeopardized by spinal cord trauma, primary disease of the nervous system, metabolic diseases such as diabetes, vascular lesions, and a host of pharmacotherapeutic agents. Explanations of the neurophysiology of penile erection in the normal and diseased state are hampered by an incomplete data base. Fundamental questions remain on the actual neurotransmitter substances responsible for vasodilation, the location of peripheral ganglionic neurons which innervate the penis, the distribution of specific nerve types within tissues of the penis and the possibility of two spinal cord centers which mediate erection. Virtually nothing is known of the changes which occur in the nerves of the penis following a lower motor neuron injury. The primary aim of the present studies is to determine the location of the various peripheral neurons which innervate the penis, the type of neurotransmitter substance they contain, and to define their distribution to the effector tissues within the penis of the rat. The second aim is to characterize the changes which may occur in the innervation of the penis following a lower motor neuron injury. This work will be accomplished by histochemical and immunocytochemical methods at the light and electron microscopic level. A focus of the proposed studies will be the localization of vasoactive intestinal polypeptide (VIP), a proposed mediator of penile erection, in neurons of the penis, and their relationship to cholinergic type terminals. In effect, the innervation of the penis will be studied as a model system in which to investigate the possibility of dual transmitter substances within the same neuron. It is anticipated that the data obtained from these studies will form a basis for understanding the physiology of penile erection. The ultimate goal will be to use this information to predict the changes which will occur in the innervation of the penis of spinally-injured man. Such data would be necessary to devise rational therapies in cases of lower motor neuron injuries.